This invention relates to 2,6-bis(3- or 4-aminophenoxy)pyridine having the following formula(I): ##STR1## (where one amino group is located in each benzene ring either at both meta- or both para- position to each oxy radical) and the method of its preparation.
More particularly, this invention relates to the above mentioned diamine (I) which is used as the material for polyimide resin having remarkably improved processing ability and adhesive strength, and the method for preparing the same.
2,6-Bis(3- or 4-aminophenoxy)pyridine has never been prepared and its use has been unknown. The derivative has been prepared for the first time by the present inventors and found to be useful for the material of polyimide. The derivative can also be applied for the raw material of polyamide and bismaleimide as well as a hardener of epoxy resin.
Polyimide has excellent properties and yet has a drawback of being difficult to process.
The present inventors investigated extensively in order to improve these drawbacks. As a result, enhancement of flexibility and easiness of processing has been found to be achieved without reduction in high-temperature stability by eliminating the linearity of polyimide structure and increasing the unit of ether linkage.
Polyimide derived from diamine derivatives having plural ether linkages at the meta-positions is regarded as the chemical structure meeting these conditions.
1,3-Bis(3-aminophenoxy)benzene has been traditionally known as a diamine derivative having such structure. Polyimide derived from this derivative has been also known to have properties of high strength and outstanding high-temperature stability.
The diamine derivative, however, has also been known to be difficult in preparation. Several processes have been known, for example; a method of preparation by condensing resorcinol with 1-bromo-3-nitrobenzene and reducing the resultant intermediate (German Pat. No. 2,462,112) and a method of preparation by the condensation of 3-aminophenol with 1,3-dibromobenzene [Helv. Chim. Acta., 51, 971(1968); U.S. Pat. No. 4,222,962]. In these methods, the diamine is prepared by using relatively low reactive materials such as 1-bromo-3-nitrobenzene and 1,3-dibromobenzene, copper-based catalysts and a large amount of solvents such as pyridine which is difficult to handle because of odor. Consequently, the yield becomes low and a great deal of expenditure and labor is consumed for the disposal of wastes and solvents, which renders the diamine derivative very expensive.
As mentioned above, polyimide derived from 1,3-bis(3-aminophenoxy)benzene has a drawback of high price, in spite of usefulness due to excellent flexibility. Therefore supply of cheap resin having good processability and high-temperature stability has been desired to achieve by overcoming these difficulties.
Furthermore, polyimide having nitrogen containing heterocyclic rings in its structure together with high-strength, high-temperature stability and other special properties has been quite unknown. The development of such resin, and thus that of derivatives for use as the raw materials have been deeply desired.